This invention relates to fuels, more particularly to oxygenated gasolines including gasolines containing a high concentration of a butanol. This invention provides an oxygenated gasoline having good driveability performance.
Gasolines are fuels which are suitable for use in a spark-ignition engine and which generally contain as a primary component a mixture of numerous hydrocarbons having different boiling points and typically boiling at a temperature in the range of from about 79° F. to about 437° F. under atmospheric pressure. This range is approximate and can vary depending upon the actual mixture of hydrocarbon molecules present, the additives or other compounds present (if any), and the environmental conditions. Typically, the hydrocarbon component of gasolines contain C4 to C10 hydrocarbons.
Gasolines are typically required to meet certain physical and performance standards. Some characteristics may be implemented for proper operation of engines or other fuel combustion apparatuses. However, many physical and performance characteristics are set by national or regional regulations for other reasons such as environmental management. Examples of physical characteristics include Reid Vapor Pressure, sulfur content, oxygen content, aromatic hydrocarbon content, benzene content, olefin content, temperature at which 90 percent of the fuel is distilled (T90), temperature at which 50 percent of the fuel is distilled (T50) and others. Performance characteristics can include octane rating, combustion properties, and emission components.
For example, standards for gasolines for sale within much of the United States are generally set forth in ASTM Standard Specification Number D 4814-07a (“ASTM D4814”) which is incorporated by reference herein. Additional federal and state regulations supplement this standard. The specifications for gasolines set forth in ASTM D4814 vary based on a number of parameters affecting volatility and combustion such as weather, season, geographic location and altitude. For this reason, gasolines produced in accordance with ASTM D4814 are broken into volatility categories AA, A, B, C, D and E, and vapor lock protection categories 1, 2, 3, 4, 5, and 6, each category having a set of specifications describing gasolines meeting the requirements of the respective classes. This specifications also sets forth test methods for determining the parameters in the specification.
For example, a Class AA-2 gasoline blended for use during the summer driving season in relatively warm climates must have a maximum vapor pressure of 7.8 psi, a maximum temperature for distillation of 10 percent of the volume of its components (the “T10”) of 158° F., a temperature range for distillation of 50 percent of the volume of its components (the “T50”) of between 170° F. and 240° F., a maximum temperature for distillation of 90 percent of the volume of its components (the “T90”) of 374° F., a distillation end point of 437° F., a distillation residue maximum of 2 volume percent, and a “Driveability Index” or “DI” maximum temperature of 1250° F. In particular, when a gasoline blend contains ethanol, ASTM D4814 uses a linear combination of D86 distillation temperatures and ethanol concentration to calculate the Driveability Index (DI), as follows:DI=1.5(T10)+3(T50)+T90+2.4(ethanol vol. %)  Equation (A)
However, control experiments have indicated that cold start and warm-up driveability performances can be problematic for gasoline blends that contain a high concentration of a butanol. It has also been found that existing methods for predicting cold start and warm-up driveability performance from fuel volatility parameters, such as the aforesaid Driveability Index (DI) are ineffective for high-butanol blends.